Method of lubricating machinery exposed to high intensity ionizing radiation



3,77,452 Patented Feb. lg, 1963 METHOD F 1. RIQATING MACERY EX- POSED TO HIGH INTENSITY ION-RING RADIATIGN Morton Z. Fainman, Glencoe, 111., assignor to Standard Gil Company, Chicago, EL, a corporation of Indiana No Drawing. Filed July 28, 1958, Ser. in. 751,131 Claims. (Cl. 252) This invention relates to lubricant oils and greases, and 10 more particularly is concerned with lubricants for use in applications where the lubricants are exposed to heavy dosages of ionizing, i.e. atomic, radiation, and in addition may be exposed to elevated temperatures.

Machinery which is exposed to atomic radiation, such as masterslave manipulators, nuclear reactor control rod drives, atomic engine pumps and turbines, and nuclear propulsion engines, requires that lubricants employed therewith be stable when subjected to heavy dosages of radiation. exposed to relatively high temperatures, frequently above 200 F. and occasionally above 400-500 F. Conventional lubricating oils are incapable of giving satisfactory performance under these service conditions, largely for o r' the reason that intense ionizing radiation causes structural perature stability. An additional object is to provide a lubricant oil which is resistant to high dosages of gamma radiation and which does not exhibit appreciable radiation-induced polymerization and consequent gum formation at high temperatures. A further object is to provide a lubricant grease containing such oil. Other and more particular objects will become apparent as the description of this invention proceeds.

In accordance with the above objects, it has now been discovered that lubricants which employ a vehicle containing a substantial amount, e.g. about or more, of hydrogenated polybutene oils are ideal lubricants for applications where heavy radiation dosages are encountered. These lubricants resist radiation-induced polymerization and thereby tend to maintain a relatively constant viscosity. The lubricant vehicle preferably is composed substantiallyentirely of hydrogenated polybutenes,

but may be a blend containing other hydrocarbon oils to form a vehicle consisting of from about 25 to about 75 volume percent of the hydrogenated polybutene and not more than about 75 percent of the other hydrocarbon oil. Lubricants which are also to be subjected to high temperatures desirably contain an oxidation inhibitor such as dilauryl selenide for improved performance. The lubricants of the present invention may be made to viscosities depending upon the particular use, ranging from about 70 SSU at 100 F. for instrument oils to 200 SSU and higher at 210 F. for heavy lubricants. They may also be thickened to grease consistency by the incorporation of a grease thickening agent.

Hydrogenated polybutene oils suitable for use in services wherein the oils are subjected to intense dosages of radiation are those oils resulting from the polymerization of butenes, predominantly isobutylene, from a butene containing stream. Such polybutenes can be obtained,

Lubricants in such applications may also be 20 Neither the 30 for example, by the polymerization in the liquid phase of a hydrocarbon mixture containing butenes at a temperature of from about F. to about F. in the presence of a Friedel-Crafts type catalyst, exemplified by boron fluoride, aluminum chloride, zinc chloride, and the like. In the preparation of these polymers, a hydrocarbon mixture containing isobutene, butenes-l and 2, and butanes recovered from petroleum gases, especially those gases produced in the cracking of petroleum oils in the manufacture of gasolines, can be used. Polymerization processes suitable for use with butane-butene streams are quite well known in the art and are fully described in such patents as U.S. 2,084,501, U.S. 2,099,090, U.S. 2,125,872, U.S. 2,269,421 and U.S. 2,677,001-2.

The original polybutene reaction product may be fractionally distilled to obtain therefrom various unhydrogenated polybutenes having viscosities ranging from about 40 to about 3,000 Saybolt Universal seconds at 210 F., corresponding to average molecular weights of from about 300 to about 1500, respectively, and several lighter fractions. The molecular structure of these polybutenes is essentially a long straight chain with methyl side groups, and one terminal double bond per molecule. The double bonds may be 'catalytically hydrogenated to materials for use in accordance with the present invention by conducting the hydrogenation of selected polybutene fractions over such well known catalysts as nickel, platinum, cobalt-molybdate, or nickel-tungsten sulfide, preferably with the catalyst extended on a high surface area support, at temperatures from about F. to about 800 F. and several hundred pounds hydrogen pressure. A slight viscosity reduction, normally less than about 5 or 10%, is occasionally experienced on hydrogenation. The hydrogenated polybutene product may be redistilled and/ or 5 steam stripped to obtain a specified flashpoint and viscosity.

Preparation of Hydrogenated Polybutene Butylenepolymer was prepared by polymerizing isobutylene in a mixed butene-butane stream at low temperature in the presence of a Friedel-Crafts catalyst. The butylene polymer thus obtained (having a viscosity of 100 SSU at 100 F.) was stripped to obtain a hydrogenation 45 feedstock having the following inspections:

Ref. index N132" 1.4739 Br, No. j 41 Vis. at 100 F, ss 53s Gravity, rr 32.4

This stock was hydrogenated over 10 percent nickel on kieselguhr catalyst at 500 p.s.i.g., a charge rate of 2.0 volumes of liquid per volume of catalyst per hour, and at a temperature of 570 F. while recycling 3,000 standard cubic feet of hydrogen per barrel of charge, and employing about 100 s.c.f./b. of hydrogen to effect hydrogenation. The hydrogenated butylene polymer had a bromine number of less than 1.0 and was fractionally distilled at 10 millimeters Hg absolute pressure and a maximum reboiler temperature of 400 F. to remove about 16 volume percent light ends as overhead and to recover a hydrogenated polybutene heart cut. This heart cut was thereafter subjected to vacuum distillation to obtain the hydrogenated polybutene fractions which were tested as radiation resistant lubricants.

To illustrate the exceptional radiation resistance of hydrogenated polybutenes, as compared to a variety of other natural and synthetic lubricants, a series of tests was conducted by measuring lubricant oil viscosity, in centistokes, both before and after subjecting the oil to a dosage of 10 roentgens of gamma irradiation from a cobalt-60 aromas .3 source under static conditions at ambient temperatures. The results are shown below:

Viscosity Change on Irradiation Viscosity, cs, at 100 F. Viscosity, cs., at 210 F.

Oil 111- In- Bel'ore After crease, Before After crease,

percent percent 1. Hydrogenated Polybutene. 117.0 65. 7 44 11.8 7. 67 31.4 2. 50% Hydrogenated Polybutone-50% Poly-WOW--. 56. 3 4t}. 6 17. 3 7. 99 6. 66 -16. 7 8. Poly-n-C'qs (162.8

S.U.S. at 100) 34. 9 37 8. 7 6. 23 6. 50 4. 4 4. Polybutene (0.1% Pans. 21. 9 18.3 16. 3. 65 3.35 8.2 5. Isooct yl Trimethyl Benzoate 8. 03 9.92 15.0 2.14 2. 40 12. 2 6. Iso-octyl Pentamethyl Benzoate 58. 4 67. 6 13. 7 5.51 5. 81 6. 4

1 Phcnylalpha-naphthylamine.

It is noted from the above table that among all the lubricants tested, only hydrogenated polybutene did not exhibit undesirable viscosity increase upon radiation. All other lubricants became more viscous, indicating a tendency of the lubricant molecules to polymerize during radiation. in run No. 2, a 50-50 volume percent blend of hydrogenated polybutene with polymerized C alpha olefin (essentially the dimer) was tested and showed that lubricant oil viscosity may be maintained essentially constant by blending hydrogenated polybutenes, which become less viscous, with another hydrocarbon which ordinarily would become more viscous; the viscosity change of the blended oil after irradiation is approximately the weighted average viscosity change of each constituent. These blends are of special value where extremely high radiation dosages are encountered, particularly at relatively low temperatures. a vehicle composition consisting of from about 25 to about 75 volume percent of hydrogenated polybutenc and up to about 75% of a hydrocarbon oil other than hydrogenated polybutene, both oils having an SUS viscosity at 210 F. of between about 40 and about 3,000. The other hydrocarbon oil may be parafiinic, naphthenic, olefinic, or aromatic, or may be a natural or synthetic mixture of hydrocarbons.

The foregoing tests were conducted with radiation at a temperature of about 70-100 F. To demonstrate the ability of hydrogenated polybutene to resist both ionizing radiation and high temperature, a sample of hydrogenated polybutene, one of unhydrogenated polybutene, and a conventional solvent-extracted SAE-40 mineral oil were each irradiated by a cobalt-60 gamma source to a dosage of between 7.2 and 7.6 megarads while being concurrently subjected to a 12-hour accelerated high temperature oxidation stability or Coker test at 545 F. Each oil was inhibited against oxidation by the addition of 5% of dilauryl selenide. This test, described without the inclusion of nuclear radiation in military procurement specification MILH8446 and Federal Test Method FTMS 791-(3), subjects the oil to heat in the presence of atmospheric oxygen while being pumped through a tube maintained at 545 F. for 12 hours. In the present test, the tube is surrounded by cobalt-60 slugs for the purpose of irradiating the oil at high temperature. Corrosion test coupons may if desired be placed at the inlet to the tube, and an oil filter is positioned at the outlet to collect sludge. At the conclusion of a test, the tube is weighed to determine the amount of coke deposit, the filter is weighed to measure the sludge formed, and the acidity of the oil is Blended lubricant oils may have determined by potassium hydroxide titration. lowing results were obtained:

Coker Test at 545 F., 12 Hours, 7.2-7.6 Megarads The for It will be observed that the solvent extracted mineral?- oil exhibited a 57% increase in viscosity caused by irradi ation, while unhydrogenated polybutene became 74% more viscous. By contrast, hydrogenated polybutene' dis-' played only a 2.7% increase in viscosity. Moreover, the coke deposition, sludge formation, and acidity of hydrogenated polybutene after being subject to the coker test were only about one-tenth of the corresponding values obtained with unhydrogenated polybutene or the mineral oil.

Hydrogenated polybutene was also exposed to the coker test with the tube at 590 F., or 45 F. higher than in the previous tests. At this higher temperature, the viscosity increase was only 5.6%, While coke and sludge formation and acidity were still well below those obtained with unhydrogenated polybutene and the mineral oil at the lower silver, and lead coupons occurred as a result of using a selenide oxidation inhibitor. Where bearings made of these materials are to be encountered, phenyl-alpha-naph thylamine, Ethyl AN-2 (a high molecular weight phenol-type inhibitor), or other inhibitors which are lesscorrosive but also suitable for use at high temperature, are preferred. Phenyl-alpha-naphthylamine and high molecular weight phenol type inhibitors are capable of providing oxidation and corrosion protection at temperatures above 400450 F and do not volatilize under these conditions.

Hydrogenated polybutenes, and mixtures of hydrogenated polybutenes with other hydrocarbon lubricants, may be thickened to grease consistency by the addition of such thickening agents as aryl substituted ureas (e.g. the reaction product of bitolylene diisocyanate with equimolar amounts of para-toluidine and para-chloro-aniline), alkali metal and alkaline earth stearates such as lithium-lZ-hy droxy stearate, or inorganic thickeners, illustratively silica aerogels and organophylic Bentones. Inorganic thickeners appear to be more stable under irradiation, and a hydrogenated polybutene grease containing 12.4% aryl substituted urea thickener experienced some thickener breakdown and became somewhat softer under a radiation dosage of 5X10 roentgens. Sodium N-octadecy1terephthalamate is a more radiation resistant organic grease. thickener and is preferred where organic-thickened greases: are desired.

In addition to oxidation inhibitors, hydrogenated polybutene liquids and greases may contain lubricity agents,

extreme pressure additives, bearing corrosion inhibitors, bloom agents, foam suppressants, and other additives commonly employed with lubricants.

From the foregoing data, it is manifest that hydrogenated polybutene oils, and oils containing substantial amounts, preferably upwards of about 25%, of hydrogenated polybutenes are exceptionally stable for use in systems wherein both ionizing radiation-gamma, neutron, alpha, or betaas well as high temperatures are encountered.

Thus having described the invention, what I claim is:

1. In the method of lubricating machinery which is exposed to high intensity ionizing radiation, the improvement which comprises lubricating said machinery with a lubricant containing at least about 25% of a hydrogenated polybutene oil, the hydrogenated polybutene oil exhibiting a characteristic decrease in viscosity when irradiated to a dosage of roentgens of gamma radiation at ambient temperature whereby said lubricant resists radiation-induced polymerization and thereby tends to resist viscosity increase upon irradiation.

2. The method of claim 1 in which said lubricant is in the form of a liquid.

3. The method of claim 1 in which said lubricant is thickened to grease consistency by the incorporation of a thickening agent.

4. The method of claim 1 in which the lubricant vehicle is composed substantially entirely of hydrogenated polybutenes.

5. In the method of lubricating machinery which is exposed to high intensity ionizing radiation and which operates at high temperatures, the improvement which comprises lubricating said machinery with a lubricant containing at least about 25% of a hydrogenated polybutene oil, the hydrogenated polybutene oil exhibiting a characteristic decrease in viscosity when irradiated to a dosage of 10 roentgens of gamma radiation at ambient temperature, and which lubricant also contains an oxi dation inhibitor suitable for use at the operating temperatures.

6. The method of claim 5 in which said oxidation inhibitor is dilauryl selenide.

7. The method of claim 5 in which said oxidation inhibitor is phenyl-alpha-naphthylamine.

8. The method of claim 6 in which said oxidation inhibitor is a high molecular Weight phenolic inhibitor.

9. In the method of lubricating machinery exposed to high intensity ionizing radiation, the improvement which comprises lubricating said machinery with a lubricant employing a vehicle consisting of from about 25 to about volume percent of a hydrogenated polybutene oil, the hydrogenated polybutene oil exhibiting a characteristic decrease in viscosity when irradiated to a dosage of 10 roentgens of gamma radiation at ambient temperature, and not more than about 75 percent of a hydrocarbon oil, other than hydrogenated polybutene, whereby said lubricant resists radiation-induced polymerization and thereby tends to maintain a substantially constant viscosity upon irradiation.

10. The method of claim 9 in which said lubricant also contains an oxidation inhibitor.

References Cited in the file of this patent I. and E. Chem., vol. 23, No. 6, June 1931, pages 604- 610.

Nature, vol. 172, July 11, 1953, pages 76 and 77. 

1. IN THE METHOD OF LUBRICATING MACHINERY WHICH IS EXPOSED TO HIGH INTENSITY IONIZING RADIATION, THE IMPROVEMENT WHICH COMPRISES LUBRICATING SAID MACHINERY WITH A LUBRICANT CONTAINING AT LEAST ABOUT 25% OF A HYDROGENATED POLYBUTENE OIL, THE HYDROGENATED POLYBUTENE OIL EXHIBITING A CHARACTERISTIC DECREASE IN VISCOSITY WHEN IRRADIATED TO A DOSAGE OF 10**8 ROENTGENS OF GAMMA RADIATION AT AMBIENT TEMPERATURE WHEREBY SAID LUBRICANT RESISTS RADIATION-INDUCED POLYMERIZATION AND THEREBY TENDS TO RESIST VISCOSITY INCREASE UPON IRRADIATION. 